Method of metal stretching, using blank-holder types of presses



P. c. PocbcK 2,

STRETCHING; USING BLANK-HOLDER TYPES OF PRESSES Nov. 24, 1942.

METHOD OF METAL Filed July 23, 1940 2 Sheets-Sheet 1 d -/3 1 1 g. 2 -5 E V i n U.

. m B401 (1 F0c0c/r MM; ATM/MEX? Patented Nov. 24, 1942 METHOD OF METAL STRETCHING, USING BLANK-HOLDER TYPES OF- PRESSES Paul C. Pocock, Mount Gilead, Ohio, assignor to The Hydraulic Development Corporation, Inc.,

Wilmington, Del., a corporation of Delaware Application July 23, 1940, Serial No. 346,944

4 Claims.v

providing a blankholder press which may selectively be used for metal stretching or metal drawing.

It is a further object of the invention to provide a blankholder press, the bed of which may adjustably receive work pieces supporting members adaptable to various sizesof work pieces to be shaped.

A still further object of the invention is to provide a pressof the type set forth in the prej ceding paragraph, in which the supporting members for the work pieces to be shaped may be used in connection with various blankholders for I drawing as well as stretching or, if desired, without removal thereof, may be adjusted so as to allow the arrangement of matching dies on the press bed for drawing or stretching.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

Figure 1 diagrammatically illustrates an embodiment of the invention.

Figure 2 is a section along the line 2-2 of Figure 1.

Figure 3 illustrates the connection of a work piece holding member to the blankholder.

Figure 4 illustrates a further embodiment of the invention. i

Figure 5 shows the arrangement of Figure 4 so adjusted as to allow the mounting of a matching die on the press bed.

Figures 6 and 7 show details of the arrangement of Figure 4.

General arrangement According to the present invention, a frame or spaced supporting members for thework piece are mounted on the press bed and the punch or form on which the metal is to be stretched is placed on the face of the pressing platen. With the press open and the blankholder extended, the

frame or supporting members, whereupon the blankholder is lowered so as to grip the sheet between the face of the blankholder and the .top of the frame or supporting members. With the blankholder holding the work piece in this position, the pressing platen pushes the form down into the sheet and forms or stretches the metal around the punch. Although in many cases the work piece may be held fast at its rim portions by exerting a correspondingly great clamping pressure on the blankholder, it may be desirable to put recesses or elevations in the surface around the edge of the frame or supporting members and corresponding recesses or elevations on the face of the blankholder or the holding members connected therewith to keep the edges of the sheet from slipping while the piece is being stretched. The provision of such recesses and elevations makes it possible to reduce the clamping pressure.

According to the method of the invention, no bottom matching die is necessary, and the punch or stretching form may be made of any responsive material that will stand the stretching pressure.

To facilitate the universal use of a standard blankholderpress for stretching as well as drawing, the supporting members for the work piece are, according to the invention, arranged on the press bed so as to allow a simple adjustment thereof, either to adapt the said supporting members to various sizes of a work piece to be shaped or to permit the arrangement of a matching die on the press bed for normal drawing operation.

When the supporting members for the work piece are provided with recesses, while the blankholder or the clamping members connected therewith are provided with elevations, the supporting members may also be used for supporting the work piece during a drawing operation, in which case only the blankholder or clamping members connected therewith are to be exchanged.

, Structural arrangement in for receiving and supporting the work piece It. Cooperating with the supportingmembers l2 are clamping members l5 connected in any consheet to be stretched is placed on top of the '55 venient manner, for instance by'screws l6 (see V dispensable and that, instead thereof, the opposing surfaces of the members I2 and i may be corrugated in any desired manner. In many cases the opposing surfaces of the members I4 and i5 may even be smooth providing that, if a stretching operation is desired, a corresponding high pressure can be exerted upon the blankholder l1 so as to prevent sliding movement of the work piece.

The clamping platen l1 has connected therewith clamping plungers [8 extending into clamping cylinders is provided in the pressing platen 20. Each clamping cylinder is is provided with a packing 2| and gland 22 for preventing leakage from said clamping cylinders.

The pressing platen 20 is provided with bores 23 adapted to receive the rods 24, the lower ends of which are secured to the blankholder or clamping platen l1, and the upper ends of which are pro vided with nuts 25 threaded thereon. The upper ends of the rods 24 are also provided with threaded sockets 26 in which are inserted the threaded rods 21. This arrangement-enables an adjustment of the effective length of the rods 24 and enables the point at which these rods 24 serve as knock-out rods to be varied as desired.

The clamping cylinders 19 are provided with passages 23 leading into tubular plungers 23 mounted upon the upper side of the pressing platen 20 and having bores 30 therethrough. The hollow plungers 29 pass through glands 3| and packings 32 compressed thereby into cylinders 33 arranged in the press head I I and within the surge tank 34, filled with fluid, and mounted on top of the press head. From each cylinder 33 leads a conduit 35 through a check valve 33 to the interior of the surge tank 34. Each check valve 35 opens in the direction of the cylinders 33 so that the latter may draw in fluid upon the descent of the hollow plungers 29. The check valves 36, however, will close upon the ascent of the plungers 23.

From each cylinder 33 leads also a T-shaped conduit 31 to a safety valve 38 and a pressure relief valve 33. These valves 38 and 33 discharge into the discharge conduit 40 leading to the interior of the surge tank 34. A pressure gauge 4| is connected with each conduit 31 by a conduit 42 to indicate the pressure existing in the clamping cylinders 19. Extending from each cylinder 33 is a conduit 43 having therein a check valve 44 opening in a direction away from the adjacent cylinder 33. Beyond the check valves 44 the conduits 43 join a common conduit 45 leading to a normally open valve 48 having a discharge conduit 41 leading therefrom to the surge tank 34. The valve 46 is provided with a valve rod 45 having an adjustable stop 49 thereon adapted to be engaged by the end 50 of a platen arm 5| secured to'the pressing platen 20.

Connected with the pressing platen 20 is the double-acting pressing plunger 52 having a piston head 53-thereon. The piston head 53 is reciprocably mounted in the pressing or main cylinder 54 associated with the press head I I. The main cylinder 54 is provided with upper and lower ports 55 and 53 on opposite sides of the piston head 53 and adapted, by means of conduits 51 and 53, to supply pressure fluid to advance or retract the plunger 52, according to the manner in which 76 the four-way valve 59 is manipulated. This valve 59 may be of any suitable type known to those skilled in the art and forms no part of the present invention.

Leading from the four-way valve 59 is the pressure conduit 80 connected at its opposite end to the pump 5|. A discharge conduit 52, also connected to the four-way valve 53, leads into the interior of the surge tank 34. The pump 5| is also provided with a suction line 63, likewise leading into the interior of the surge tank 34. The main cylinder 54 is provided, near the mouth of its bore 64, with a packing ring 55, beyond which is a packing, 66 adapted to be compressed by a gland 51 so as to prevent leakage around the plunger 52.

As will be seen from Figures 1 and 2, the supporting members H are slidably mounted on the press bed I5 by means of slide blocks 63 and bolts 53 with nuts 10. The slide blocks 68 are adapted to slide in T-slots 1| in the press bed.

While in the embodiment of Figures 1 and 2 only two supporting members i2 are shown, which would be quite sufflcient if metal strips are to be stretched, it is, of course, understood that also supporting members connecting the supporting members l2, or arranged therebetween, may be provided. To this end, a hollow cast iron frame may be set on the bed of the press and connected therewith, or the arrangement of Figure 4 may be selected. According to Figure 4 the transverse supporting members 12 are hinged by means .of a hinge 13 to the press bed I lie, whereas the longitudinal supporting members 14 are slidably mounted in T-slots 15 provided in the press bed Ilia. In this instance it is possible to use only the supporting members 14 in which case the supporting members 12 are lowered, as indicated in Figure 6, or, if desired, the supporting members 14, together with the supporting members 12, may be employed. In the last mentioned instance the supporting members 12 are lifted, as indicated in Figure '7, so as to lie between the supporting members 14. The supporting members 14 may be held in their desired position in a similar manner as the supporting members l2 shown in Figures 1 and 2.

If it is desired to effect a normal drawing opera-- In the operation of the form of press shown in 4 Figure 1, the pump 51 is started in any convenient manner and delivers pressure fluid to the four-way valve 53 which, in turn, is set to deliver pressure fluid through the conduit 51 and port 55 into the space above the piston head 53. This pressure forces the pressing plunger 52 and the pressing platen 20 connected therewith downwardly, carrying with them the blankholder or clamping platen l1 with the clamping members l5 and the hollow plungers 29. The suction thereby created in the cylinders 33 opens the check valves and causes fluid to be drawn into the cylinders from the surge tank 34. When the blankholder or clamping platen l1 descends to a point where the clamping members l5 connected therewith engage the work piece l4, however, a relative motion occurs between the now halted blankholder l1 and the pressing platen 20 as the latter continues to advance and move its drawing die or punch 11, supported by the platen 20, into engagement with the workpiece l4,

Pressure thus accumulates in the clamping cylinders l9 and is transmitted through the passages 28 of the hollow plungers 29 into the cylinders 33. Normally, this pressure would be free to pass through the conduits 43, check valves 44, conduit 45, normally open valve 46 and conduit 41 into the surge tank 34. By this time, however, the platen 20 has descended to a point where the end 50 of the platen arm 5| has engaged the stop and moves the valve rod 48 downwardly, thereby closing the normally open valve 46 and cutting off this means of escape for the fluid from the cylinders 33. The check valves 36 in the conduits 35v also close against the pressure in the,

cylinders 33. This leaves the conduits 31 as the sole means of escape for the fluid. Consequently, when'the pressure in each conduit 31 exceeds the setting of its relief valve 39, the latter will open and discharge fluid through its' discharge conduit 49 into the surge tank 34. In the event that the pressure relief valve 39 jams, or fails for other reasons, the safety valve 38, which is 'set for a higher pressure, will openand discharge the fluidthereby preventing damage to the press. By adjusting the, relief valves 39 to discharge at different pressures, the clamping cylinders l9 and the clamping plungers l8 may be caused to exert different clamping pressures on the periphery of the work piece l4 so that selectively the rim portion of the work piece l4 may be clamped, either so asto allow a sliding movement thereof or not to allow such sliding movement, depending on whether a drawing or stretching operation is desired. It is, of course, also possible to adjust theindividual relief valves so as to cause the blankholder to apply different amounts of pressure to different points on the periphery of the work piece. In this instance, the check valves 44 prevent the equalization of pressure between the several cylinders 33. Consequently, the intensified pressure built up in the clamping cylinders l9 acts against the clamping plungers l 8 to clamp the work piece l4. At the same time a portion of this pressure fluid passing through the bore 28 of each hollow plunger 29 acts against the annular top surface thereof and urges each plunger 29 in a downward direction, thereby assisting the action of the main plunger 52, which causes' the punch 11 to shape the work piece l4.

As soon as the shaping operation has been completed, the operator shifts the four-way control valve 59 to cause the pump 6| to discharge pressure fluid through the conduit 58 into the space beneath the piston head 53. This pressure raises the pressing plunger 52 and the platen 20, together with the hollow plungers 29. At the start of this operation, however, the platen arm 5| is still holding the normally open valve 46 in a closed position,hence, the plungers 29 can not return against-the pressure'already built up in the cylinders 33'without displacing fluid into the clamping cylinders [9 within the platen 20. This pressure fiuid, so displaced, actsagainst the clamping plungers l8 and tends-to separate the platen 20 and the blankholder I'I until both have traveled a distance suflicient to enable the platen arm5l to release the stop 49 upon the valve rod 48 and permit the valve 46 to resume its normal open position, for instance, by means of a spring urging said valve toward open position. When this occurs the fluid can escape from the cylinders 33 through the conduit 43, the check valves 44 and the conduit 41 into the surge tank 34,

new work piece therefor, a new cycle maybe started.

As previously mentioned if, instead of the stretching operation illustrated in Figure 1, a

drawing operation is to be performed, the supporting members I2 are moved away from each other so as to allow the insertion of a lower die 16, as illustrated in Figure 5. The platen l! is then replaced by a platen Ha, while the operation of the press is the same as described inconnection with Figure -1.

Although the present invention has been described in connection with a blankholder press of the type shown in Figure 1 it is, of course, understood-that any other type of blankholder press may be used in connection with the present invention. By a blankholder press" is meant a press having a stationary base member for supporting a blank, a hydraulic cylinder, a plunger therein, a platen operated by the plunger and the usual clamping piston and cylinder assemblies. I

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention.-

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In combination in a press, a press bed, supporting members mounted on said press bed for supporting rim portions of a. work piece, said supporting members being hinged to said press bed so as selectively to allow movement of said supporting members into a position substantially flush withthe upper surface of said bed or into a position protruding beyond said upper bed surface for spacing a work piece therefrom, a pressing platen, and a, blankholder operatively connected with said pressing platen, said blankholder being provided with clamping portions for selectively clamping rim portions of a work piece against said supporting member.

2. In combination in a press, a press bed, a supporting frame for supporting rim portions of a work piece, said frame having two pairs of side members, one pair of which is hinged to said bed-and adapted selectively to be moved into a recess in said bed, while the other pair of said side members is detachably connected to said'bed and movable in a direction transverse to the side members of said first pair, a pressing platen, a punch supported by said pressing platen for shaping a work piece, and a blankholder op-.

eratively connected with said pressin platen and 7 porting a metal sheet, each of said supportingv members having a substantially plane surface -portion and a' grooved surface portion, said to receive a rim portion of said metal sheet, a

press platen for subjecting said metal sheet toa shaping operation, a reciprocable blankholder having a substantially plane surface adapted to clamp a rim portion of said metal sheet against said plane surface portion of said supporting means so asto permit a limited sliding movement of said metal sheet relative to said'blankholder during the shaping operation, and holding means detachably connected to said plane surface of said blankholder and adapted to' enter said grooved surface portions-of said supporting members for holding said metal sheet clamped therebetween so as selectively to prevent said clamped metal sheet portion from sliding.

4. A method of metal stretching on a hydraulic blankholder press, which comprises the steps of' placing a work-piece upon spaced supporting members, preliminarily engaging the workpiece on adjacent marginal portions thereof to hold the same in proper position, exerting stretchingpressure onsthat part of the workpiece between and spaced from said supporting members without supporting the center portion of said workpiece, while simultaneously conveying a portion of the stretching pressure to the workpiece to greatly increase the clamping pressure on the marginal portions of the workpiece and causing deformation of at least a part of the marginal portions of the workpiece to hold the latter in clamped immovable position during the stretching operation.

PAUL C. POCOCK. 

